During prohibition, alcohol wasn't supposed to be in the country, either. But there was a market for alcohol, just as there is a market for illegal labor.
My bigger point is that measures like this are aimed at hurting the supply of illegals. But we'll never fix the problem unless we reduce the demand for illegal labor. As long as the demand for something exists, there will always be a supply.
Of course the real source of the problem is our government intentionally had lax border enforcement for years to provide that cheap labor.